18. e2e3 In return for the exchange, White has the bishop pair, a great knight on d4, pressure on the queenside, and the black knight is trapped on a2. The computer gives its traditional equality assessment, but in practice the position is difficult to play for Black. Some positions are \"more equal\" than others. 18... f6d5  19. h1d1 [%c_effect d1;square;d1;type;GreatFind;persistent;true] Another important move to protect the d4-knight and make the e3-e4 advance available in case the poor piece on a2 tries to run away. 19... d5b4  20. g2b7 